A solenoid spool valve includes a spool valve, a spring, and an electromagnetic actuator. The spool valve has a generally cylindrical sleeve provided with input and output ports, and a spool supported axially slidably within the sleeve to switch between the input and output ports. The spring serves as an energizer that abuts against one end face of the spool to push the spool back toward the electromagnetic actuator. The electromagnetic actuator is a linear actuator that applies a driving axial force to the other end face of the spool to push the spool axially toward one side against the energizing force exerted by the spring (e.g., see Japanese Patent Laid-Open Publication No. 2001-108135).
An inclination or misalignment of the spring may cause a diagonal force on the spool. Likewise, an inclination or misalignment of a pressure-applying member (e.g., a shaft or a member for transferring a force produced on the plunger of the electromagnetic actuator to the spool) may also cause a diagonal force on the spool. Here, the sleeve includes bearings for slidably supporting the spool. The bearing has a clearance between the spool and the sleeve for allowing the spool to slide.
The inclination of the spool is restricted at both of the axial end portions of the bearing (at the outermost ends of all the bearings supporting the spool). However, the conventional spool valve was configured such that portions (working faces) subjected to the forces of the spring and the electromagnetic actuator were disposed outside the both axial end portions of the bearing. Thus, the points of effort force (the working faces) stayed outside the fulcrums (the outer end portions of the bearing). In this arrangement, an inclination or misalignment of the spring or the pressure-applying member would cause a radial load (a force pushing the bearing) imposed by the spool on the bearing to increase based on the principle of lever.
On the other hand, many examples exist in which part of the spool protrudes excessively from the axial end portion of the bearing. The spool having an excessively protruded portion from the axial end of the bearing would cause a heavy radial load on the bearing due to the weight of the protruded portion. The heavy radial load imposed by the spool on the bearing causes part of the bearing and part of the spool to rub hard against each other resulting in an increase in friction, thereby impeding smooth movement of the spool.
Furthermore, the working faces acted upon by the forces of the spring and the electromagnetic actuator stayed axially outside the bearing, thereby causing an increase in entire length of the spool valve.